The present invention relates to a damping apparatus for preventing transmission of mechanical vibrations (vibration isolation) and/or controlling mechanical vibrations (damping).
The active damping apparatus utilizing an oscillating element as an actuator for transformation of electrical oscillation into mechanical oscillation has been disclosed in Japanese Laid-open Patent Specifications No. 63-53617 and No. 63-261300. In these systems, an actuator-load sensor series is interposed between two structures at least one of which is a source of vibration and an acceleration sensor is mounted on the vibration source structure. According to this system, the mechanical vibration of a vibration source structure is transformed into an electric oscillation and the oscillating element is driven in accordance with the output electric oscillation signal. The underlying principle is that the mechanical vibration of a vibration source is cancelled by active mechanical oscillation of the actuator to preclude propagation of the source vibration. As an example of the oscillating element, there by may be mentioned a stack of piezoelectric ceramic wafers of plates.
The stacked piezoelectric ceramic oscillating element used in the above damping device, however, does provide only a minuscular dimensional change of about 1 .mu.m at the maximum per mm of the element. On the other hand, the amplitude of the mechanical oscillation of the automotive engine damping mount, for instance, is generally .+-. about 0.5 mm to .+-. about 0.05. Therefore, in order to prevent transmission of the mechanical vibration of an engine to the body of the motor vehicle by means of said conventional active damping device, one would have to employ an oscillating element as large as 10 cm to even 1 m, which is near to impossibility.
It is, therefore, a first object of the invention to provide an active damping apparatus employing an oscillating element capable of converting an electric oscillating signal to a mechanical oscillation, which is capable of attenuating the large-amplitude mechanical vibrations of vibration source structures.
A hitherto-known damping apparatus for automotive and equivalent use comprises a housing constituted by a resilient wall and a cup-shaped wall, a fluid chamber defined by these walls and a diaphragm disposed in the housing and an orificed plate disposed in the fluid chamber. This damping apparatus is able to cope with vibrations of low frequencies in the neighborhood of 10 Hz, such as shake vibrations, by resonance of the liquid column in the orifice but can hardly attenuate vibrations in any selected and wide range of frequency band, including idling and other vibrations of frequencies in the neighborhood of 30 Hz, vibrations in the neighborhood of 100 Hz such as trapped sounds, or high-frequency vibrations in the vicinity of a few hundred Hz such as transmission sounds.
It is, therefore, a second object of the present invention to provide a damping apparatus which can selectively cope with any of low-frequency, large-amplitude vibration, intermediate-frequency, intermediate-amplitude vibration, and high-frequency, small amplitude vibration.
As one of the known damping apparatuses, there is a cylindrical engine mount.
FIG. 59 is a view illustrating a mode of application of the conventional cylindrical engine mount to an FF type motor vehicle.
As shown, a cylindrical engine mount 610 is supported by a metal member 604 secured to the engine by way of a shaft 606. The outer side of the engine mount 610 is supported by a metal member 612 secured to the vehicle body. In the conventional engine mount as shown, an inner cylinder 620 is eccentrically located within an outer cylinder 621 and these inner and outer cylinders are bridged by resilient elastomer 622 and by the shaft 606 passed into the inner cylinder 620, this inner cylinder 620 is supported on the metal 604 on the engine side while the outer cylinder 621 is supported on the metal 612 on the vehicle body. Thus, a rubber-like elastomer 622 is interposed between the inner cylinder 620 which oscillates with the engine and the outer cylinder rigidly secured to the body through the intervening material. However, as the engine load is applied to the inner cylinder 620 the elastomer deforms to bring the inner cylinder 620 into a substantially concentric position with respect to the outer cylinder 621. As shown in FIG. 60, a construction wherein a resilient elastomer is filled between the inner and outer cylinders 620, 621 is also known.
As aforesaid, the vibrations of an engine run the whole gamut from shake vibrations in the neighborhood of 10 Hz during driving and vibrations in the neighborhood of 30 Hz during idling to high-frequency vibrations in the vicinity of several hundreds of Hz.
However, the above conventional cylindrical engine mount 610 including resilient elastic embers 622, 623 between the inner and outer cylinders 620, 621 cannot sufficiently attenuate the low-frequency vibrations.
Therefore, a fluid-seal cylindrical engine mount as shown in FIG. 61 has recently come into use. In this engine mount 610, the eccentrically disposed inner and outer cylinders 620, 621 are internally bridged by resilient elastomer 622 to define a couple of radially juxtaposed fluid compartments 624, 625 which are communicating with each other through an orifice 626. In this fluid-seal cylindrical engine mount 610, low-frequency vibrations are attenuated by the flow of the fluid through the orifice 626 on input of vibration.
As an example of the actuator which generates a mechanical oscillation, there is known an oscillating element comprising a stack of piezoelectric ceramics. However, since there has been no cylindrical engine mount which performs positive damping of engine vibrations by the active mechanical oscillation of an actuator, no prior art devices offer a free choice of damping characteristics.
It is, therefore, a third object of the present invention to provide an active cylindrical damping apparatus containing a built-in actuator.
A further example of the cylindrical fluid-seal engine mount for an FF motor vehicle is illustrated in FIG. 72. In this engine mount 910, an inner cylinder 914 is eccentrically disposed in an outer cylinder 912 and the two cylinders 912 and 914 are bridged by supporting rubber 916. The outer cylinder 912 and supporting rubber 916 define a first fluid compartment 918, while a second compartment 924 is defined by the outer cylinder 912 and a diaphragm 922 supported by a stopper 920 secured to the edge of the supporting rubber 916 on the opposite side with respect to said first fluid chamber. Disposed slightly inwardly of the inner circumferential wall of the outer cylinder 912 is a divider 926 which extends from the first fluid chamber to the second fluid chamber. This divider 926 has ports 928, 930 opening into the two fluid compartments 918, 924, respectively, thus forming a circumferential orifice 930 through which the first fluid compartment and the second fluid compartment are intercommunicated. The outer cylinder is connected to the body of the motor vehicle, while the inner cylinder is connected to the engine side.
In the cylindrical engine mount illustrated in FIG. 72, low-frequency and intermediate-frequency vibrations can be attenuated by resonance of the liquid column in the circumferential orifice 930 but high-frequency vibrations cannot be adequately suppressed.
It is, therefore, a fourth object of the present invention to provide a cylindrical damping apparatus which can cope with both low-frequency and high-frequency vibrations (in common with the second object).